1. Field of the Invention
The present invention relates to latex emulsions, coating compositions formed from latex emulsions, methods of coating substrates with the coating compositions, and substrates coated with the coating compositions.
2. Description of Related Art
Coating compositions formed from epoxy resins have been used to coat packaging and containers for foods and beverages. Although the weight of scientific evidence, as interpreted by the major global regulatory food safety agencies in the US, Canada, Europe, and Japan, shows that the levels of bisphenol A consumers are exposed to with current commercial epoxy based coatings is safe, some consumers and brand owners continue to express concern, and a coating that does not contain bisphenol A or any other endocrine disruptor is desirable.
International Publication No. WO 2008/036629 discloses a coating composition for food and beverage containers composed of a grafted polyester-acrylate resin that is crosslinked with a phenolic crosslinker and catalyzed by a titanium-containing or zirconium-containing catalyst.
U.S. Patent Application Publication No. 2005/0196629 also discloses a coating composition for food and beverage containers composed of a grafted polyester-acrylate resin that is crosslinked with a phenolic crosslinker.
U.S. Patent Application Publication No. 2006/0100366 uses an acrylic polymer as a dispersant for latex polymerization by combining an ethylenically unsaturated monomer component with a dispersion of a salt of an acid- or anhydride-functional polymer and an amine to form an emulsion.
U.S. Patent Application Publication No. 2007/0117928 and U.S. Pat. No. 7,189,787 disclose the formation of a dispersion which is the reaction product of a tertiary amine with an acid functional polymer and a glycidyl functional polymer.
International Publication No. WO 2007/123659 discloses a coating composition formed by crosslinking an acrylic polymer having a molecular weight greater than 41,000 and an acid value less than 30 mg KOH/g.
U.S. Patent Application Publication No. 2007/0281179 discloses a coating composition having a polyester which is the reaction product of a polyol and a bis-epoxy reacted with a mono- and/or di-phenolic carboxylic acid and/or ester.
Latexes made by emulsion polymerization have not achieved the performance of epoxy based coatings and have not been successfully used on a commercial basis in food and beverage coating compositions. Some drawbacks have been flavor acceptance in beer and blush performance in pasteurized or retorted hard-to-hold beverages. Typical latex emulsion polymers use sodium salts as buffers and stabilizers, and/or non ionic surfactants which also impart an unacceptable degree of sensitivity to water (blushing).
There is a need to produce coating compositions that do not contain bisphenol A or are substantially free of bisphenol A. The latex emulsions of the invention can be used in the preparation of coating compositions suitable, inter alia, as packaging coatings for food and beverage packaging and containers, including beer and beverage external/interior easy-open-ends. Easy-open-ends for beer and beverage cans are typically manufactured by first coating a flat sheet of a metal substrate, heating the coated substrate, and then stamping or shaping the coated substrate into the desired shape. The coatings for beer and beverage can ends may be applied in film weights of about 1 milligram per square inch to about 15 milligrams per square inch on a high speed coil coating line. High speed coil coating lines require a coating material that will dry and cure within a few second as it is heated very rapidly to a peak metal temperature that can range from about 200 to about 300° C.